1. Field of the Invention
The present invention relates generally to a detector for charged particles including a plurality of particle sensitive regions.
2. Description of the Related Art
When a primary particle beam strikes a solid, secondary particles are emitted due to the interaction of the primary particles with the material of the solid. The energy distribution and angular distribution of the secondary particles are dependent on, among other things, the chemical and/or physical composition present at the interaction region, on the surface structure, and on the distribution of voltages present on the specimen. The secondary electrons triggered at surface proximate regions are of special significance for imaging in scanning electron microscopes.
The secondary electrons are documented, for example, with a detector arranged laterally above the specimen to be imaged. As a consequence of the asymmetrical arrangement of the detector which is usually composed of an extraction electrode, a scintillator, and of a light conductor within the specimen chamber, the detection probability of the secondary electrons and, thus, the signal level measured in the detector is decisively influenced by the point at which the secondary electrons are triggered on the specimen. See, for example, the Journal of Scientific Instruements, Volume 37, July 1960, pages 246 through 248.
A detector system including a plurality of individual detectors is disclosed in European Pat. No. 0 018 031. Such a multi-detector system is mainly used for investigating large area specimens to guarantee a largly symmetrical extraction of the secondary electrons which is independent of emission location and emission angle. These detector arrangements, however, have the disadvantage that a noise signal generated by back-scattered electrons is superimposed on the measured secondary electron signal. This is due to the total detector area which is multiplied in comparison to that of individual detectors.